arXiv subjects

Gabriela Canalizo

Publications and source records attributed to Gabriela Canalizo.

At least 55 records · Page 3Linked to original sources

arXiv2019

AGN-Driven Outflows in Dwarf Galaxies

We present spatially resolved kinematic measurements of AGN-driven outflows in dwarf galaxies in the stellar mass range $\sim6\times10^8 - 9\times10^9 M_\odot$, selected from SDSS DR7,8 and followed up with Keck/LRIS spectroscopy. We find spatially extended ($\sim 1$ half light radius), high velocity ionized gas outflows ($W_{80}$ up to $\sim2000\,\rm{km\,s}^{-1}$) in 13/50 dwarf galaxies with and without AGN. Outflow velocities in all 13 galaxies exceed the escape velocities of their halos. Nine of these 13 galaxies are classified as AGN according to their narrow line flux ratios. Of these, six have outflow components with emission line ratios consistent with AGN ionization. Although black holes have been known to populate the centers of at least a few dwarf galaxies, and indirect evidence of AGN quenching of star formation in dwarfs has begun to surface, our measurements constitute the first direct detection and measurement of AGN impact on the large scale kinematics and gas content in dwarf galaxies. Furthermore, we find evidence suggestive of ongoing star formation suppression, possibly regulated by the AGN. Galaxy formation models must therefore be able to account not only for the formation and growth of black holes at the centers of dwarf galaxies, but should also be revised to include AGN as important -- and perhaps dominant -- sources of feedback in low mass galaxies

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arXiv2019

High-resolution Infrared Spectrograph for Exoplanet Characterization with the Keck and Thirty Meter Telescopes

HISPEC (High-resolution Infrared Spectrograph for Exoplanet Characterization) is a proposed diffraction-limited spectrograph for the W.M. Keck Observatory, and a pathfinder for the MODHIS facility project (Multi-Object Diffraction-limited High-resolution Infrared Spectrograph) on the Thirty Meter Telescope. HISPEC/MODHIS builds on diffraction-limited spectrograph designs which rely on adaptively corrected single-mode fiber feeds. Seeing-limited high-resolution spectrographs, by virtue of the conservation of beam etendue, grow in volume following a D^3 power law (D is the telescope diameter), and are subject to daunting challenges associated with their large size. Diffraction-limited spectrographs fed by single mode fibers are decoupled from the telescope input, and are orders of magnitude more compact and have intrinsically stable line spread functions. Their efficiency is directly proportional to the performance of the adaptive optics (AO) system. AO technologies have matured rapidly over the past two decades and are baselined for future extremely large telescopes. HISPEC/MODHIS will take R>100,000 spectra of a few objects in a 10" field-of-view sampled at the diffraction limit (~10-50 mas), simultaneously from 0.95 to 2.4 microns (y-K). The scientific scope ranges from exoplanet infrared precision radial velocities, spectroscopy of transiting, close-in, and directly imaged exoplanets (atmospheric composition and dynamics, RM effect, spin measurements, Doppler imaging), brown dwarf characterization, stellar physics/chemistry, proto-planetary disk kinematics/composition, Solar system, extragalactic science, and cosmology. HISPEC/MODHIS features a compact, cost-effective design optimized to fully exploit the existing Keck-AO and future TMT-NFIRAOS infrastructures and boost the scientific reach of Keck Observatory and TMT soon after first light.

astro-ph.IM↗

arXiv2019

A Triple AGN in a Mid-Infrared Selected Late Stage Galaxy Merger

The co-evolution of galaxies and the supermassive black holes (SMBHs) at their centers via hierarchical galaxy mergers is a key prediction of $Λ$CDM cosmology. As gas and dust are funneled to the SMBHs during the merger, the SMBHs light up as active galactic nuclei (AGNs). In some cases, a merger of two galaxies can encounter a third galaxy, leading to a triple merger, which would manifest as a triple AGN if all three SMBHs are simultaneously accreting. Using high-spatial resolution X-ray, near-IR, and optical spectroscopic diagnostics, we report here a compelling case of an AGN triplet with mutual separations < 10 kpc in the advanced merger SDSS J084905.51+111447.2 at z = 0.077. The system exhibits three nuclear X-ray sources, optical spectroscopic line ratios consistent with AGN in each nucleus, a high excitation near-IR coronal line in one nucleus, and broad Pa$α$ detections in two nuclei. Hard X-ray spectral fitting reveals a high column density along the line of sight, consistent with the picture of late-stage mergers hosting heavily absorbed AGNs. Our multiwavelength diagnostics support a triple AGN scenario, and we rule out alternative explanations such as star formation activity, shock-driven emission, and emission from fewer than three AGN. The dynamics of gravitationally bound triple SMBH systems can dramatically reduce binary SMBH inspiral timescales, providing a possible means to surmount the "Final Parsec Problem." AGN triplets in advanced mergers are the only observational forerunner to bound triple SMBH systems and thus offer a glimpse of the accretion activity and environments of the AGNs prior to the gravitationally-bound triple phase.

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arXiv2019

Stronger Constraints on the Evolution of the $M_{\rm{BH}}-σ_*$ Relation up to $z\sim0.6$

We revisit the possibility of redshift evolution in the $M_{\rm{BH}}-σ_*$ relation with a sample of 22 Seyfert 1 galaxies with black holes (BHs) in the mass range $10^{6.3}-10^{8.3}~M_\odot$ and redshift range $0.03<z<0.57$ with spectra obtained from spatially resolved Keck/Low-Resolution Imaging Spectrometer observations. Stellar velocity dispersions were measured directly from the Mg Ib region, taking into consideration the effect of Fe II contamination, active galactic nucleus (AGN) dilution, and host-galaxy morphology on our measurements. BH masses are estimated using the H$β$ line width, and the luminosity at 5100 $\overset{\lower.5em\circ}{\mathrm{A}}$ is estimated from surface brightness decomposition of the AGN from the host galaxy using high-resolution imaging from the Hubble Space Telescope. Additionally, we investigate the use of the [O III]$\lambda5007$ emission line width as a surrogate for stellar velocity dispersion, finding better correlation once corrected for Fe II contamination and any possible blueshifted wing components. Our selection criteria allowed us to probe lower-luminosity AGNs and lower-mass BHs in the non-local universe than those measured in previous single-epoch studies. We find that any offset in the $M_{\rm{BH}}-σ_*$ relation up to $z\sim0.6$ is consistent with the scatter of local BH masses, and address the sources of biases and uncertainties that contribute to this scatter.

astro-ph.GA↗

arXiv2019

On the origin of star-gas counterrotation in low-mass galaxies

Stars in galaxies form from the cold rotationally supported gaseous disks that settle at the center of dark matter halos. In the simplest models, such angular momentum is acquired early on at the time of collapse of the halo and preserved thereafter, implying a well-aligned spin for the stellar and gaseous component. Observations however have shown the presence of gaseous disks in counterrotation with the stars. We use the Illustris numerical simulations to study the origin of such counterrotation in low mass galaxies ($M_\star = 2 \times 10^9$ - $5 \times 10^{10}\; \rm M_\odot$), a sample where mergers have not played a significant role. Only ${\sim}1\%$ of our sample shows a counterrotating gaseous disk at $z=0$. These counterrotating disks arise in galaxies that have had a significant episode of gas removal followed by the acquisition of new gas with misaligned angular momentum. In our simulations, we identify two main channels responsible for the gas loss: a strong feedback burst and gas stripping during a fly-by passage through a more massive group environment. Once settled, counterrotation can be long-lived with several galaxies in our sample displaying misaligned components consistently for more than $2$ Gyr. As a result, no major correlation with the present day environment or structural properties might remain, except for a slight preference for early type morphologies and a lower than average gas content at a given stellar mass.

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arXiv2018

Medium-resolution Optical and Near-Infrared Spectral Atlas of 16 2MASS-selected NIR-red Active Galactic Nuclei at $z \sim 0.3$

We present medium-resolution spectra ($R \sim 2000$--4000) at 0.4--1.0\,$μ$m and 0.7--2.5\,$μ$m of 16 active galactic nuclei (AGNs) selected with red color in the near-infrared (NIR) of $J - K > 2.0$ mag at $z \sim 0.3$. We fit the H$β$, H$α$, P$β$, and P$α$ lines from these spectra to obtain their luminosities and line widths. We derive the $E(B-V)$ color excess values of the NIR-red AGNs using two methods, one based on the line-luminosity ratios and another based on the continuum slopes. The two $E(B-V)$ values agree with each other at rms dispersion $\sim$ 0.249. About half of the NIR-red AGNs have $g'-K < 5$ magnitude, and we find that these NIR red, but blue in optical-NIR AGNs, have $E(B-V) \sim 0$, suggesting that a significant fraction of the NIR color-selected red AGNs are unobscured or only mildly obscured. After correcting for the dust extinction, we estimate the black hole (BH) masses and the bolometric luminosities of the NIR-red AGNs using the Paschen lines to calculate their Eddington ratios ($λ_{\rm Edd}$). The median Eddington ratios of nine NIR-red AGNs ($\log (λ_{\rm Edd}) \simeq -0.654 \pm 0.176$) are only mildly higher than those of unobscured type 1 AGNs ($\log (λ_{\rm Edd}) \simeq -0.961 \pm 0.008$). Moreover, we find that the $M_{\rm BH}$--$σ_{\ast}$ relation for three NIR-red AGNs is consistent with that of unobscured type 1 AGNs at similar redshift. These results suggest that the NIR red color selection alone is not effective at picking up dusty, intermediate-stage AGNs.

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arXiv2018

Keck OSIRIS AO LIRG Analysis: Feedback in the Nuclei of Luminous Infrared Galaxies

The role of feedback in triggering or quenching star formation and hence driving galaxy evolution can be directly studied with high resolution integral field observations. The manifestation of feedback in shocks is particularly important to examine in galaxy mergers, where violent interactions of gas takes place in the interstellar medium during the course of the galactic collision. As part of our effort to systematically study the local population of luminous infrared galaxies within the Great Observatories All-Sky LIRG Survey, we undertook the Keck OSIRIS AO LIRG Analysis observing campaign to study the gas dynamics in the inner kiloparsec regions of these systems at spatial scales of a few 10s of parsecs. With high-resolution near-infrared adaptive optics-assisted integral-field observations taken with OSIRIS on the Keck Telescopes, we employ near-infrared diagnostics such as Brg and the ro-vibrationally excited H2 lines to quantify the nuclear star formation rate and identify feedback associated with shocked molecular gas seen in 21 nearby luminous infrared galaxies. Shocked molecular gas is preferentially found in the ultraluminous infrared systems, but may also be triggered at a lower luminosity, earlier merging stage. On circumnuclear scales, AGN have a strong effect on heating the surrounding molecular gas, though their coupling is not simply driven by AGN strength but rather is complicated by orientation, dust shielding, density, and other factors. We find that the nuclear star formation correlates with merger class and diminishing projected nuclear separations. These trends are largely consistent with the picture of merger-induced starbursts within the center of galaxy mergers.

astro-ph.GA↗

arXiv2018

The Lick AGN Monitoring Project 2011: Dynamical Modeling of the Broad-Line Region

We present models of the H$β$-emitting broad-line region (BLR) in seven Seyfert 1 galaxies from the Lick AGN (Active Galactic Nucleus) Monitoring Project 2011 sample, drawing inferences on the BLR structure and dynamics as well as the mass of the central supermassive black hole. We find that the BLR is generally a thick disk, viewed close to face-on, with preferential emission back toward the ionizing source. The dynamics in our sample range from near-circular elliptical orbits to inflowing or outflowing trajectories. We measure black hole masses of $\log_{10}(M_{\rm BH}/M_\odot) = 6.48^{+0.21}_{-0.18}$ for PG 1310$-$108, $7.50^{+0.25}_{-0.18}$ for Mrk 50, $7.46^{+0.15}_{-0.21}$ for Mrk 141, $7.58^{+0.08}_{-0.08}$ for Mrk 279, $7.11^{+0.20}_{-0.17}$ for Mrk 1511, $6.65^{+0.27}_{-0.15}$ for NGC 4593, and $6.94^{+0.14}_{-0.14}$ for Zw 229$-$015. We use these black hole mass measurements along with cross-correlation time lags and line widths to recover the scale factor $f$ used in traditional reverberation mapping measurements. Combining our results with other studies that use this modeling technique, bringing our sample size to 16, we calculate a scale factor that can be used for measuring black hole masses in other reverberation mapping campaigns. When using the root-mean-square (rms) spectrum and using the line dispersion to measure the line width, we find $\log_{10}(f_{{\rm rms},σ})_{\rm pred} = 0.57 \pm 0.19$. Finally, we search for correlations between $f$ and other AGN and BLR parameters and find marginal evidence that $f$ is correlated with $M_{\rm BH}$ and the BLR inclination angle, but no significant evidence of a correlation with the AGN luminosity or Eddington ratio.

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arXiv2017

Detection of Prominent Stellar Disks in the Progenitors of Present-day Massive Elliptical Galaxies

Massive galaxies at higher redshifts ($\emph{z}$ $>$ 2) show different characteristics from their local counterparts: They are compact and most likely have a disk. In this study, we trace the evolution of local massive galaxies by performing a detailed morphological analysis, namely, fitting single Sérsic profiles and performing bulge+disk decompositions. We analyze $\sim$ 250 massive galaxies selected from all CANDELS fields (COSMOS, UDS, EGS, GOODS-South and GOODS-North). We confirm that both star-forming and quiescent galaxies increase their sizes significantly from $\emph{z}$ $\approx$ 2.5 to the present day. The global Sérsic index of quiescent galaxies increases over time (from $n$ $\approx$ 2.5 to $n$ $>$ 4), while that of star-forming galaxies remains roughly constant ($n$ $\approx$ 2.5). By decomposing galaxy profiles into bulge+disk components, we find that massive galaxies at high redshift have prominent stellar disks, which are also evident from visual inspection of the images. By $z$ $\approx$ 0.5, the majority of the disks disappear and massive quiescent galaxies begin to resemble the local elliptical galaxies. Star-forming galaxies have lower bulge-to-total ratios ($B/T$) than their quiescent counterparts at each redshift bin. The bulges of star-forming and quiescent galaxies follow different evolutionary histories, while their disks evolve similarly. We conclude that major mergers, along with minor mergers, have played a crucial role in the significant size increase of high-\emph{z} galaxies and the destruction of their massive and large-scale disks.

astro-ph.GA↗

arXiv2016

Stellar Velocity Dispersion in Mergers: The Effects of Dust and Star Formation

We investigate the effects of stellar evolution and dust on measurements of stellar velocity dispersion in mergers of disk galaxies. $N$-body simulations and radiative transfer analysis software are used to obtain mass-weighted and flux-weighted measurements of stellar velocity dispersion. We find that the distribution of dust with respect to the distribution of young stars in such systems is more important than the total degree of attenuation. The presence of dust typically causes flux-weighted measurements of stellar velocity dispersion to be elevated with respect to mass-weighted measurements because dust preferentially obscures young stars, which tend to be dynamically cooler than older stellar populations in such systems. In exceptional situations, in which young stars are not preferentially obscured by dust, flux-weighted velocity dispersion measurements tend to be negatively offset with respect to mass-weighted measurements because the dynamically cool young stellar populations are more luminous, per unit mass, than older stellar populations. Our findings provide a context for comparing observationally-obtained measurements of velocity dispersion with measurements of velocity dispersion obtained from galaxy merger simulations.

astro-ph.GA↗

arXiv2014

Kinematics of Stellar Populations in Post-Starburst Galaxies

Post-starburst galaxies host a population of early-type stars (A or F), but simultaneously lack indicators of ongoing star formation such as OII emission. Two distinct stellar populations have been identified in these systems: a young post-starburst population superimposed on an older host population. We present a study of nine post-starburst galaxies with the following objectives: 1) to investigate if and how kinematical differences between the young and old populations of stars can be measured; and 2) to gain insight into the formation mechanism of the young population in these systems. We fit high signal-to-noise spectra with two independent populations in distinct spectral regions: the Balmer region, the MgIb region, and the Ca Triplet when available. We show that the kinematics of the two populations largely track one another if measured in the Balmer region with high signal-to-noise data. Results from examining the Faber-Jackson relation and the Fundamental Plane indicate these objects are not kinematically disturbed relative to more evolved spheroids. A case-study of the internal kinematics of one object in our sample shows it to be pressure-supported and not rotationally-dominated. Overall our results are consistent with merger-induced starburst scenarios where the young population is observed during the later stages of the merger.

astro-ph.GA↗

arXiv2014

Detection of Galactic Center source G2 at 3.8 $μ$m during periapse passage

We report new observations of the Galactic Center source G2 from the W. M. Keck Observatory. G2 is a dusty red object associated with gas that shows tidal interactions as it nears closest approach with the Galaxy's central black hole. Our observations, conducted as G2 passed through periapse, were designed to test the proposal that G2 is a 3 earth mass gas cloud. Such a cloud should be tidally disrupted during periapse passage. The data were obtained using the Keck II laser guide star adaptive optics system (LGSAO) and the facility near-infrared camera (NIRC2) through the K' [2.1 $μ$m] and L' [3.8 $μ$m] broadband filters. Several results emerge from these observations: 1) G2 has survived its closest approach to the black hole as a compact, unresolved source at L'; 2) G2's L' brightness measurements are consistent with those over the last decade; 3) G2's motion continues to be consistent with a Keplerian model. These results rule out G2 as a pure gas cloud and imply that G2 has a central star. This star has a luminosity of $\sim$30 $L_{\odot} $ and is surrounded by a large ($\sim$2.6 AU) optically thick dust shell. The differences between the L' and Br-$γ$ observations can be understood with a model in which L' and Br-$γ$ emission arises primarily from internal and external heating, respectively. We suggest that G2 is a binary star merger product and will ultimately appear similar to the B-stars that are tightly clustered around the black hole (the so-called S-star cluster).

astro-ph.HE↗

arXiv2014

Stellar Velocity Dispersion in Dissipative Galaxy Mergers with Star Formation

In order to better understand stellar dynamics in merging systems, such as NGC 6240, we examine the evolution of central stellar velocity dispersion (\sig) in dissipative galaxy mergers using a suite of binary disk merger simulations that include feedback from stellar formation and active galactic nuclei (AGNs). We find that $σ_*$ undergoes the same general stages of evolution that were observed in our previous dissipationless simulations: coherent oscillation, then phase mixing, followed by dynamical equilibrium. We also find that measurements of $σ_*$ that are based only upon the youngest stars in simulations consistently yield lower values than measurements based upon the total stellar population. This finding appears to be consistent with the so-called "$σ_*$ discrepancy," observed in real galaxies. We note that quasar-level AGN activity is much more likely to occur when $σ_*$ is near its equilibrium value rather than during periods of extreme $σ_*$. Finally, we provide estimates of the scatter inherent in measuring $σ_*$ in ongoing mergers.

astro-ph.GA↗

arXiv2013

Intermediate-Age Stellar Populations in Classical QSO Host Galaxies

Although mergers and starbursts are often invoked in the discussion of QSO activity in the context of galaxy evolution, several studies have questioned their importance or even their presence in QSO host galaxies. Accordingly, we are conducting a study of z~0.2 QSO host galaxies previously classified as passively evolving elliptical galaxies. We present deep Keck LRIS spectroscopy of a sample of 15 hosts and model their stellar absorption spectra using stellar synthesis models. The high S/N of our spectra allow us to break various degeneracies that arise from different combinations of models, varying metallicities, and contamination from QSO light. We find that none of the host spectra can be modeled by purely old stellar populations and that the majority of the hosts (14/15) have a substantial contribution from intermediate-age populations with ages ranging from 0.7 to 2.4 Gyr. An average host spectrum is strikingly well fit by a combination of an old population and a 2.1 (+0.5, -0.7) Gyr population. The morphologies of the host galaxies suggest that these aging starbursts were induced during the early stages of the mergers that resulted in the elliptical-shaped galaxies that we observe. The current AGN activity likely corresponds to the late episodes of accretion predicted by numerical simulations, which occur near the end of the mergers, whereas earlier episodes may be more difficult to observe due to obscuration. Our off-axis observations prevent us from detecting any current star formation or young stellar populations that may be present in the central few kiloparsecs.

astro-ph.CO↗

arXiv2013

Mid-infrared Spectral Properties of Post-Starburst Quasars

We present Spitzer InfraRed Spectrograph (IRS) low-resolution spectra of 16 spectroscopically selected post-starburst quasars (PSQs) at z ~ 0.3. The optical spectra of these broad-lined active galactic nuclei (AGNs) simultaneously show spectral signatures of massive intermediate-aged stellar populations making them good candidates for studying the connections between AGNs and their hosts. The resulting spectra show relatively strong polycyclic aromatic hydrocarbon (PAH) emission features at 6.2 and 11.3\micron and a very weak silicate feature, indicative of ongoing star formation and low dust obscuration levels for the AGNs. We find that the mid-infrared composite spectrum of PSQs has spectral properties between ULIRGs and QSOs, suggesting that PSQs are hybrid AGN and starburst systems as also seen in their optical spectra. We also find that PSQs in early-type host galaxies tend to have relatively strong AGN activities, while those in spiral hosts have stronger PAH emission, indicating more star formation.

astro-ph.CO↗

arXiv2013

The Lick AGN Monitoring Project 2011: Fe II Reverberation from the Outer Broad-Line Region

The prominent broad Fe II emission blends in the spectra of active galactic nuclei have been shown to vary in response to continuum variations, but past attempts to measure the reverberation lag time of the optical Fe II lines have met with only limited success. Here we report the detection of Fe II reverberation in two Seyfert 1 galaxies, NGC 4593 and Mrk 1511, based on data from a program carried out at Lick Observatory in Spring 2011. Light curves for emission lines including H-beta and Fe II were measured by applying a fitting routine to decompose the spectra into several continuum and emission-line components, and we use cross-correlation techniques to determine the reverberation lags of the emission lines relative to V-band light curves. In both cases the measured lag (t_cen) of Fe II is longer than that of H-beta, although the inferred lags are somewhat sensitive to the choice of Fe II template used in the fit. For spectral decompositions done using the Fe II template of Veron-Cetty et al. (2004), we find t_cen(Fe II)/t_cen(H-beta) = 1.9+-0.6 in NGC 4593 and 1.5+-0.3 in Mrk 1511. The detection of highly correlated variations between Fe II and continuum emission demonstrates that the Fe II emission in these galaxies originates in photoionized gas, located predominantly in the outer portion of the broad-line region.

astro-ph.CO↗

arXiv2013

The Low-Luminosity End of the Radius-Luminosity Relationship for Active Galactic Nuclei

We present an updated and revised analysis of the relationship between the Hbeta broad-line region (BLR) radius and the luminosity of the active galactic nucleus (AGN). Specifically, we have carried out two-dimensional surface brightness decompositions of the host galaxies of 9 new AGNs imaged with the Hubble Space Telescope Wide Field Camera 3. The surface brightness decompositions allow us to create "AGN-free" images of the galaxies, from which we measure the starlight contribution to the optical luminosity measured through the ground-based spectroscopic aperture. We also incorporate 20 new reverberation-mapping measurements of the Hbeta time lag, which is assumed to yield the average Hbeta BLR radius. The final sample includes 41 AGNs covering four orders of magnitude in luminosity. The additions and updates incorporated here primarily affect the low-luminosity end of the R-L relationship. The best fit to the relationship using a Bayesian analysis finds a slope of alpha = 0.533 (+0.035/-0.033), consistent with previous work and with simple photoionization arguments. Only two AGNs appear to be outliers from the relationship, but both of them have monitoring light curves that raise doubt regarding the accuracy of their reported time lags. The scatter around the relationship is found to be 0.19(+/-0.02) dex, but would be decreased to 0.13 dex by the removal of these two suspect measurements. A large fraction of the remaining scatter in the relationship is likely due to the inaccurate distances to the AGN host galaxies. Our results help support the possibility that the R-L relationship could potentially be used to turn the BLRs of AGNs into standardizable candles. This would allow the cosmological expansion of the Universe to be probed by a separate population of objects, and over a larger range of redshifts.

astro-ph.CO↗

arXiv2012

The Properties of Post-Starburst Quasars Based on Optical Spectroscopy

We present optical spectroscopy of a sample of 38 post-starburst quasars (PSQs) at z ~ 0.3, 29 of which have morphological classifications based on Hubble Space Telescope imaging. These broad-lined active galactic nuclei (AGNs) possess the spectral signatures of massive intermediate-aged stellar populations making them potentially useful for studying connections between nuclear activity and host galaxy evolution. We model the spectra in order to determine the ages and masses of the host stellar populations, and the black hole masses and Eddington fractions of the AGNs. Our model components include an instantaneous starburst, a power-law, and emission lines. We find the PSQs have MBH ~ 10^8 Msun accreting at a few percent of Eddington luminosity and host ~ 10^10.5 Msun stellar populations which are several hundred Myr to a few Gyr old. We investigate relationships among these derived properties, spectral properties, and morphologies. We find that PSQs hosted in spiral galaxies have significantly weaker AGN luminosities, older starburst ages, and narrow emission-line ratios diagnostic of ongoing star-formation when compared to their early-type counterparts. We conclude that the early-type PSQs are likely the result of major mergers and were likely luminous infrared galaxies in the past, while spiral PSQs with more complex star-formation histories are triggered by less dramatic events (e.g., harassment, bars). We provide diagnostics to distinguish the early-type and spiral hosts when high spatial resolution imaging is not available.

astro-ph.CO↗